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In this study, we assimilated microwave (MW) all‐sky radiances from low‐Earth‐orbiting satellites and examined their impact on the analyses and forecasts of weather hazards associated with the 10 August 2020 Midwest derecho. Compared with the baseline that assimilated conventional surface and upper‐air observations and infrared (IR) all‐sky radiances from geostationary satellites, the addition of MW all‐sky radiances improved the analyzed and forecasted convection‐stratiform structures of the derecho. Results show that MW all‐sky radiances provided additional information, compared with IR radiances, on hydrometeors within the storm, leading to improved forecasts out to 2 hr with quantitatively more accurate surface gusts. This is the first study to assimilate MW all‐sky radiances for a severe weather event using a convection‐permitting numerical weather prediction model (our model resembles NOAA's High‐Resolution Rapid Refresh), and the results suggest promising avenues for improving severe weather forecasts worldwide in the future. Plain Language Summary: Satellite observations are the backbone of modern weather forecast operations, especially for severe weather monitoring and prediction. However, they are also severely underutilized by computer weather models. Many satellite observations impacted by clouds and precipitation are not used in these models, despite their ability to characterize important features of ongoing severe weather events. This study focuses on satellite observations at microwave (MW) frequencies that are impacted by clouds and precipitation. We explore their potential benefits by incorporating them into a computer weather model using data assimilation and examining their impact on severe weather forecasts. We utilize the 10 August 2020 Midwest derecho that produced extensive wind damage as a case study. Because these MW observations contain contributions from precipitating particles within the derecho, assimilating these observations yields better depictions of the derecho structure in the computer model. Consequently, more accurate forecasts of surface gusts are produced. The results of this study suggest a promising avenue for improving severe weather forecasts worldwide in the future, especially for regions that lack the resources and infrastructure to support high‐spatiotemporal‐resolution weather observations. Key Points: Microwave (MW) all‐sky radiances are impacted by hydrometeors within clouds, complementing cloud‐top dominated infrared all‐sky radiancesAssimilating MW all‐sky radiances leads to improved storm structure in the analyses of the 10 August 2020 Midwest derechoWith improved depiction of the derecho's structure, accurate gust forecasts are obtained 2 hr earlier [ABSTRACT FROM AUTHOR]

This study explores how tornadic supercell soundings significantly differ from the same‐location and same‐hour baseline environment soundings, sampled from the days prior to or following the event. Permutation testing is used to identify whether sounding‐derived parameters mixed‐layer convective available potential energy and 0–1 km storm‐relative helicity are significantly different between the tornadic and baseline environment. Typically, in an environment with marginal values of certain key environmental parameters, anomalous values of those environmental parameters are more strongly associated with supercell tornadoes. Furthermore, many tornadic events already exhibit environmental conditions favorable for tornadic supercells a day prior to the event itself. Generally, supercell tornadoes that occur during typical peak tornadic activity time frames are easier to distinguish from baseline (non‐tornadic) environments compared to those occurring in other time frames. Spatiotemporal variations of distinguishability between tornadic and baseline environmental parameters add complexity to traditional parameter‐based fixed threshold forecasting. Plain Language Summary: We use simple hypothesis testing to understand how unusual the environments of especially powerful supercell tornadoes actually are, compared to non‐tornadic environments that are nearby in space and time. This approach can provide insights as to where and when atmospheric models are performing better or worse. Based on two environmental parameters related to atmospheric instability and low‐level rotation, we find that a portion of the environments that are favorable for tornadoes already exist a day prior to the actual event. Furthermore, the degree of difficulty in distinguishing supercell tornadic environments from typical non‐storm environments varies in different regions and at different times. This work highlights the need to develop region‐specific and potentially time‐specific environmental baseline evaluations to improve forecast and warning skill. Key Points: We compared the near‐storm environments of tornadic supercells to baseline non‐storm environments using hypothesis testingThe environments of supercell tornadoes that occur outside of peak tornado times more closely resemble those of baseline environmentsDiscrimination of tornadic environments is improved by increasing sample sizes of days prior to tornado and number of baseline environments [ABSTRACT FROM AUTHOR]

Radar‐derived refractivity provides moisture information near the surface, which plays a crucial role in convective initiation and of heavy rain. In this study, the high‐resolution Weather Research and Forecasting local ensemble transform Kalman filter data assimilation system was employed for two cases in the Southwest Monsoon Experiment to conduct two experimental sets. The first set was applied in both cases to investigate the effects of assimilating radar‐retrieved refractivity along with reflectivity and radial wind. The second set was conducted in the second case to examine the benefit of increasing the frequency of refractivity assimilation and investigate the optimal strategy to assimilate refractivity. Results of the two cases revealed that assimilating reflectivity and radial velocity modified near‐surface humidity on the basis of the flow‐dependent error correlation estimated by the ensemble, but the spatial distribution may not be fully accurate, causing underestimation of rainfall. With further refractivity assimilation, stronger convergence and more accurate low‐level moisture, temperature, and wind field corrections were obtained, leading to superior forecasts for both light and heavy rainfall during six hours. The results of the second set indicated that increasing the assimilation interval of refractivity enabled capturing the dramatic moisture variation and enhancing wind convergence, resulting in short‐term forecast improvement. The strategy that solely assimilated refractivity before the appearance of the convection system optimized the correction of environmental moisture, then accurately represented the humidity and strengthened the wind convergence when precipitation occurred. Consequently, the achieved improvement of the short‐term forecast was most noteworthy, particularly for heavy rain. [ABSTRACT FROM AUTHOR]

We present the System for High‐resolution prediction on Earth‐to‐Local Domains (SHiELD), an atmosphere model developed by the Geophysical Fluid Dynamics Laboratory (GFDL) coupling the nonhydrostatic FV3 Dynamical Core to a physics suite originally taken from the Global Forecast System. SHiELD is designed to demonstrate new capabilities within its components, explore new model applications, and to answer scientific questions through these new functionalities. A variety of configurations are presented, including short‐to‐medium‐range and subseasonal‐to‐seasonal prediction, global‐to‐regional convective‐scale hurricane and contiguous U.S. precipitation forecasts, and global cloud‐resolving modeling. Advances within SHiELD can be seamlessly transitioned into other Unified Forecast System or FV3‐based models, including operational implementations of the Unified Forecast System. Continued development of SHiELD has shown improvement upon existing models. The flagship 13‐km SHiELD demonstrates steadily improved large‐scale prediction skill and precipitation prediction skill. SHiELD and the coarser‐resolution S‐SHiELD demonstrate a superior diurnal cycle compared to existing climate models; the latter also demonstrates 28 days of useful prediction skill for the Madden‐Julian Oscillation. The global‐to‐regional nested configurations T‐SHiELD (tropical Atlantic) and C‐SHiELD (contiguous United States) show significant improvement in hurricane structure from a new tracer advection scheme and promise for medium‐range prediction of convective storms. Plain Language Summary: At many weather forecasting centers where computer weather models are run, different models are run for different applications. However, each separate model multiplies the effort needed to maintain and upgrade each model and makes it difficult to move improvements between models. We present a new "unified" weather modeling system, System for High‐resolution prediction on Earth‐to‐Local Domains, able to be configured for a variety of applications. This system uses a powerful computer code, FV3, to compute the fluid motion of the atmosphere at any scale and also able to zoom in on areas of interest to better "see" severe storms or intense hurricanes. We show how we started from a quickly assembled model for testing FV3 and then gradually improved the representation of different atmospheric processes and expanded into new uses for the system, including short‐range severe thunderstorm prediction, hurricane forecasting, and forecasts out to as long as 6 weeks. We address some of the challenges that we faced and discuss prospects for future model improvements. Since many of the parts of System for High‐resolution prediction on Earth‐to‐Local Domains are used by models being developed by the National Weather Service for use by weather forecasters, the advances described here can be rapidly introduced into those models, eventually improving official forecasts. Key Points: A unified "one code, one executable, one workflow" global prediction modeling system is presentedSHiELD's multiple configurations show prediction skill and simulation fidelity matching or exceeding those of existing U.S. modelsThe FV3 Dynamical Core provides a powerful foundation for unified prediction modeling [ABSTRACT FROM AUTHOR]

We present a comprehensive study of the three-dimensional structure of the Novorossiysk bora, a severe downslope windstorm on the north-eastern coast of the Black Sea. The analysis is based on observational data obtained from the Russian Hydrometeorological Service, automatic weather stations, sodar system, microwave temperature profiler and 10-m mast. In addition, WRF-ARW simulations are performed to verify and complement the observations. The data permit us to investigate major features of the flow over mountain ridges during several bora episodes. The qualitative and quantitative characteristics of the Novorossiysk bora were compared with those of other downslope winds, such as the Adriatic bora, the Boulder windstorm, and the Alpine foehn. [ABSTRACT FROM AUTHOR]

Owing to the complex mesoscale meteorological dynamics, deep basin topography and pollutants emissions, the Chengdu Plain (CDP) situated at west border of the Sichuan Basin (SCB) have suffered excessive ozone (O 3) pollution in the warm season. However, the meteorology-driven mechanism and associated dominant processes underlying the elevated O 3 levels are not well elucidated due to limited ambient measurements. Here, we adopted trace gases data measured by basin-wide network in combination with a high-resolution chemical transport model for characterizing a regional continuous O 3 episode occurred from 10 to 18 August 2019. The extensive monitoring network shapes a much-detailed evolution map of O 3 concentrations which depicts that O 3 hotspots extend from metropolitan areas to suburban areas across the CDP. It is found that both advection of O 3 -rich air masses in the residual layer (RL) and regional transport of O 3 and its precursors under prevailing winds exert profound influences on the elevation of ambient O 3 across the CDP. As the convective boundary layer is destroyed after sunrise, vertical mixing effects cause the entrainment of O 3 -rich air masses in RL to the surface, affecting the redistribution of surface O 3 concentration. In addition, process analysis (PA) and integrated source apportionment method (ISAM) results of the CMAQ model indicated that vertical transport and gas-phase chemistry were the main sources of O 3 during the day, while dry deposition and horizontal advection were the main sinks of surface O 3. O 3 transport by boundary condition (BCO) was the largest contributor to all urban O 3 concentrations in the CDP. Our findings highlight the regional transport mechanism of O 3 in SCB under complex topographic conditions and point out the physical and chemical causes and sources of typical summer O 3 pollution episodes in the SCB. [Display omitted] • Spatial evolution of O 3 was analyzed with an intensive urban monitoring dataset. • The prevailing wind fields govern the transport of O 3 in the residual layer. • Advanced modeling reveal the meteorology-driven mechanism of O 3 pollution. • Sources and geographic features determine spatial evolution in O 3 episode. [ABSTRACT FROM AUTHOR]

ABSTRACT Ozone and particle pollution are of concern for the Sydney basin, in particular during warm months (November to March) when pollution levels can exceed national standards. Previous studies on the relationship between synoptic circulation and air quality focused on high pollution days or aggregated air quality conditions over the region as a whole. This study provides both temporal and spatial analyses of the synoptic processes affecting warm-month ozone and particle pollution in Sydney. A warm-month synoptic catalogue was developed by applying the self-organising map method to the NCEP/NCAR geopotential height reanalysis for south-east Australia. The catalogue was linked to mesoscale meteorological features such as drainage flows and sea breezes, and subsequently to the spatial variability in air quality across the Sydney basin. The typical synoptic types commonly associated with high or low ozone and PM10 levels, as well as variations in visibility, were identified. The results suggest that, due to Sydney's subtropical coastal-basin environment, the interaction between meso- and synoptic-scale features determine local air quality conditions in the region, rather than the synoptic conditions alone. Emissions from bushfires appear to have considerable impacts on the synoptic modulation to visibility and PM10 levels, with such impacts tending to be more at a local scale. In contrast, no comparable impacts were found for ozone pollution. For ozone and visibility, the probability for an exceedance day under some synoptic types varied considerably over time, implying that there might have been a shift in the role of synoptic modulation to local air quality associated with changes in air emissions profiles. This study provides a leap in our understanding of the relationship between synoptic circulation and air quality in a coastal-basin environment. The results are useful for improving air quality forecasting in Sydney, with the methodology developed readily applicable to similar regions elsewhere. [ABSTRACT FROM AUTHOR]

In this study, reanalysis and regional atmospheric modelling was used to resolve the climatology and mesoscale structure, spatial variability and temporal characteristics of the Oman coastal low-level jet (CLLJ). The limited area model COAMPS® was used at a 6-km horizontal resolution for a 5-month period (May–September) during 2009. Analysis of high-resolution model fields reveals the mesoscale structure of the Oman CLLJ, clearly distinguishing it from the large-scale South Asia monsoon circulation farther offshore, and from the previously identified Findlater (or Somali) jet, which occurs at a higher altitude. The Oman CLLJ is closer to the coast and spreads northeastward along the coast of Oman, clearly interacting with the coastal topography and headlands. It has a very strong annual cycle, related to the South Asia monsoon, with July exhibiting the highest CLLJ frequency of occurrence (around 80%) and highest wind speeds (around 27 ms−1), and May and September being the transition months. The southerly location of the Oman CLLJ, along with the very strong inland summer heating in the Arabian Peninsula, affects its diurnal cycle, with highest number of occurrences early in the morning, whereas the highest wind speeds occur during late afternoon, setting this CLLJ apart from other coastal jets in mid-latitude areas along eastern boundary currents. [ABSTRACT FROM AUTHOR]

The tropical cyclone (TC) track and intensity predictions over Bay of Bengal (BOB) using the Advanced Research Weather Research and Forecasting (ARW) model are evaluated for a number of data assimilation experiments using various types of data. Eight cyclones that made landfall along the east coast of India during 2008-2013 were simulated. Numerical experiments included a control run (CTL) using the National Centers for Environmental Prediction (NCEP) 3-hourly 0.5×0.5° resolution Global Forecasting System (GFS) analysis as the initial condition, and a series of cycling mode variational assimilation experiments with Weather Research and Forecasting (WRF) data assimilation (WRFDA) system using NCEP global PrepBUFR observations (VARPREP), Atmospheric Motion Vectors (VARAMV), Advanced Microwave Sounding Unit (AMSU) A and B radiances (VARRAD) and a combination of PrepBUFR and RAD (VARPREPCRAD). The impact of different observations is investigated in detail in a case of the strongest TC, Phailin, for intensity, track and structure parameters, and finally also on a larger set of cyclones. The results show that the assimilation of AMSU radiances and Atmospheric Motion Vectors (AMV) improved the intensity and track predictions to a certain extent and the use of operationally available NCEP PrepBUFR data which contains both conventional and satellite observations produced larger impacts leading to improvements in track and intensity forecasts. The forecast improvements are found to be associated with changes in pressure, wind, temperature and humidity distributions in the initial conditions after data assimilation. The assimilation of mass (radiance) and wind (AMV) data showed different impacts. While the motion vectors mainly influenced the track predictions, the radiance data merely influenced forecast intensity. Of various experiments, the VARPREP produced the largest impact with mean errors (India Meteorological Department (IMD) observations less the model values) of 78, 129, 166, 210 km in the vector track position, 10.3, 5.8, 4.8, 9.0 hPa deeper than IMD data in central sea level pressure (CSLP) and 10.8, 3.9, -0:2, 2.3 m s-1 stronger than IMD data in maximum surface winds (MSW) for 24, 48, 72, 96 h forecasts respectively. An improvement of about 3-36% in track, 6-63% in CSLP, 26-103% in MSW and 11-223% in the radius of maximum winds in 24-96 h lead time forecasts are found with VARPREP over CTL, suggesting the advantages of assimilation of operationally available PrepBUFR data for cyclone predictions. The better predictions with PrepBUFR could be due to quality-controlled observations in addition to containing different types of data (conventional, satellite) covering an effectively larger area. The performance degradation of VARPREPCRAD with the assimilation of all available observations over the domain after 72 h could be due to poor area coverage and bias in the radiance data. [ABSTRACT FROM AUTHOR]

A Himalayan cloudburst event, which occurred on 3 August 2012 in the Uttarkashi (30.73° N, 78.45° E) region of Uttarakhand, India, was analyzed. The near-surface atmospheric variables were analyzed to study the formation, evolution, and triggering mechanisms of this cloudburst. In order to improve upon the understanding provided by the observations, numerical simulations were performed using the Weather Research and Forecasting (WRF) model, configured with a single domain at 18 km resolution. The model was tuned using variation of different parameterizations (convective, microphysical, boundary layer, radiation, and land surface), and different model options (number of vertical levels, and spin-up time), which resulted in a combination of parameters and options that best reproduced the observed diurnal characteristics of the near-surface atmospheric variables. Our study demonstrates the ability of WRF in forecasting precipitation, and resolving synoptic-scale and mesoscale interactions. In order to better understand the cloudburst, we configured WRF with multiply nested two-way-interacting domains (18, 6, 2 km) centered on the location of interest, and simulated the event with the best configuration derived earlier. The results indicate that two mesoscale convective systems originating from Madhya Pradesh and Tibet interacted over Uttarkashi and, under orographic uplifting and in the presence of favorable moisture condition, resulted in this cloudburst event. [ABSTRACT FROM AUTHOR]

Numerical experiments are performed using the WRF model to investigate which category of model physics is most critical for a proper simulation of the structure and intensity of a Mediterranean hurricane. Several combinations are used, and the model outputs are compared with the available observations and a reference simulation. The choice of microphysics scheme, and in a minor way, of cumulus parameterization, has the greatest impact on the model results. Boundary layer schemes and land–surface models appear to play only a marginal role. The ability of the model to reproduce the evolution of the cyclone from extra-tropical to tropical-like (TLC) is also explored. Apart from a few experiments differing for the microphysical scheme, all simulations are able to reproduce the cyclone features properly, and identify the presence of tropical characteristics, i.e. a symmetric, deep warm core, in the later stage of the cyclone lifetime, but with duration and intensity depending on the experiment. The motivation for the failure in some simulations is traced back to the incorrect representation of the cyclone location along its transit in the southern Ionian Sea, before its transition to TLC. In this phase, the interaction of the intense easterly flow, developing on the northern side of the cyclone, with the Apennines near the coasts of Calabria is fundamental for the later intensification of the cyclone, due to the severe convection triggered by the orographic uplift. Thus, an even small misplacement of the simulated cyclone during this phase may dramatically affect its following evolution. For the sake of comparison with the multi-physics approach, a time-lagged ensemble, with initial conditions starting at different times, is also considered. The spread in the cyclone depth and track in the latter case is smaller or comparable with that emerging in experiments using different microphysical schemes, but is larger compared with the experiments changing the other categories of parameterization schemes. [ABSTRACT FROM AUTHOR]

Using a fully nonlinear two-dimensional (2-D) numerical model, we simulated gravity waves (GWs) breaking and their contributions to the formation of large winds and wind shears in the mesosphere and lower thermosphere (MLT). An eddy diffusion coefficient is used in the 2-D numerical model to parameterize realistic turbulent mixing. Our study shows that the momentum deposited by breaking GWs accelerates the mean wind. The resultant large background wind increases the GW's apparent horizontal phase velocity and decreases the GW's intrinsic frequency and vertical wavelength. Both the accelerated mean wind and the decreased GW vertical wavelength contribute to the enhancement of wind shears. This, in turn, creates a background condition that favors the occurrence of GW instability, breaking, and momentum deposition, as well as mean wind acceleration, which further enhances the wind shears. We find that GWs with longer vertical wavelengths and faster horizontal phase velocity can induce larger winds, but they may not necessarily induce larger wind shears. In addition, the background temperature can affect the time and height of GW breaking, thus causing accelerated mean winds and wind shears. [ABSTRACT FROM AUTHOR]

One of the important mechanisms of stratosphere-troposphere exchange, which brings ozone-rich stratospheric air to low altitudes in extratropical regions, is transport related to tropopause folds. The climatology of folds has been studied at high latitudes of the Northern Hemisphere with the help of radars and global models. Global models supply information about fold occurrence rates at high latitudes of the Southern Hemisphere as well, but so far comparisons with direct measurements are rare. The Moveable Atmospheric Radar for Antarctica (MARA), a 54.5MHz wind-profiler radar, has been operated at the Norwegian year-round station Troll, Antarctica (72° S, 2.5°E) since December 2011. Frequent tropopause fold signatures have been observed. In this study, based on MARA observations, an occurrence rate statistics of tropopause folds from December 2011 until November 2012 has been made, and radar data have been compared with the analysis from the European Center for Medium-Range Weather Forecasting (ECMWF). The fold occurrence rates exhibit an annual cycle with winter maximum and summer minimum and suggest significantly higher occurrence rates for the given location than those obtained previously by global model studies. [ABSTRACT FROM AUTHOR]

Abstract: Two case studies of intense lee waves generated by the interaction of the atmospheric flow with the orography over an area in the eastern Mediterranean Sea, located east of Crete and south of Rhodes islands, are analyzed using the Weather Research and Forecasting (WRF) model. The model has been implemented in two different configurations, using distinct boundary layer parametrization schemes, the Yonsei University (YSU) and the Mellor–Yamada–Janjic (MYJ) schemes, and three 2-way nested domains, the inner one covering the area of interest with a horizontal resolution of 1km. The model-derived wind fields have been compared with the sea surface wind extracted from Envisat Advanced Synthetic Aperture Radar (ASAR) images, from which the wind has been retrieved using a methodology based on the two-dimensional continuous wavelet transform. In the first case, the trains of atmospheric gravity waves, individuated by the signature in the ASAR image, extend downstream for more than 150km and are realistically simulated in the two model configurations, although some appreciable differences are present. The wavelength spectra of the wind speed from ASAR and the two WRF runs have been calculated along different transects in the area affected by atmospheric gravity waves. The agreement is satisfactory, and the difference in wavelengths among the different wave trains generated by the orographic obstacles is well represented in the model runs. Among the two simulations, the YSU run performs better than MYJ. The latter result is consistent with the fact that the YSU experiment reproduces the observed wind profile and the Scorer parameter profile better than the MYJ run. The second case study is briefly analyzed to test the generality of the results of the first event. In this case, part of the wave energy is distributed at larger scales, due to the interaction of the flow with the Peloponnese. Again, both model configurations are able to reproduce correctly the wave patterns, but in this case the difference between the two model runs is negligible. [Copyright &y& Elsevier]

High spatial and temporal variability of mesoscale moisture fields is still a challenge for quantitative precipitation forecast within numerical weather prediction (NWP) models especially over ocean regions where observations are lacking. This study presents the comparison between integrated water vapor over the Mediterranean Sea determined from shipborne GPS, the NWP ALADIN/Météo-France model and MODIS retrieval during a 4-month campaign (autumn 2008). While moisture prediction of the NWP remains accurate during most of the observation period, there are significant periods with offsets between GPS data and model predictions. We analyze such events and discuss the associated meteorological situation. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Abstract: Terrestrial and Martian atmospheres are both characterised by a large variety of mesoscale meteorological events, occurring at horizontal scales of hundreds of kilometres and below. Available measurements from space exploration and recently developed high-resolution numerical tools have given insights into Martian mesoscale phenomena, as well as similarities and differences with their terrestrial counterparts. The remarkable intensity of Martian mesoscale events compared to terrestrial phenomena mainly results from low density and strong radiative control. This is exemplified in the present paper by discussing two mesoscale phenomena encountered in the lowest atmospheric levels of both planets with notable differences: nighttime katabatic winds (drainage flow down sloping terrains) and daytime boundary layer convection (vertical growth of mixed layer over heated surfaces). While observations of katabatic events are difficult on Earth, except over vast ice sheets, intense clear-cut downslope circulations are expected to be widespread on Mars. Convective motions in the daytime Martian boundary layer are primarily driven by radiative contributions, usually negligible on Earth where sensible heat flux dominates, and exhibit turbulent variances one order of magnitude larger. Martian maximum heat fluxes are not attained close to the surface as on Earth but a few hundreds of metres above, which implies generalised definitions for mixing layer scales such as vertical velocity w ⁎. Measurements on Mars of winds in uneven topographical areas and of heat fluxes over flat terrains could be useful to assess general principles of mesoscale meteorology applicable to both terrestrial and Martian environments. [Copyright &y& Elsevier]

Abstract: An unusually intense subsynoptic-scale cyclone has been documented in southeastern Italy on 26 September 2006. Numerical simulations are performed with the Weather Research and Forecasting model (WRF). Model results show that the model is able to realistically capture the timing and intensity of the cyclone, identifying in this small-scale cyclone the typical characteristics of a Mediterranean tropical-like cyclone. Sensitivity experiments to sea surface temperature (SST) of the simulated cyclone are discussed in the present paper. In these experiments the SST was changed by a constant few degrees uniformly throughout the Mediterranean Sea. The simulated-cyclone sensitivity to SST is studied in the framework of an air–sea interaction theory, in particular during the two phases that are fundamental for the development of an environment favorable to severe convection and thus for the cyclone to be self-sustained. The modifications of the properties of the simulated cyclones are then analyzed using an objective evaluation, based on a phase diagram used to study the tropical–extratropical transition of cyclones. The present simulations show that the features typical of a tropical cyclone are progressively lost as the SST is reduced. In the colder SST experiments, the lower intensity of the sea-surface fluxes has the effect of delaying and reducing the development of convection and the intensification of the cyclone, so that the cyclone loses the characteristics of a tropical cyclone when SST is reduced by more than 4°C. On the other hand, the cyclone shows a pressure minimum deeper than the control run, with a persistent symmetric warm core, for SST increased by more than 2°C. Finally, when SST is changed by less than 2°C, the cyclone depth and trajectory are not significantly affected by the change in SST and, like the control run, show tropical-like features only for a limited period. [Copyright &y& Elsevier]

The Regional Atmospheric Modeling System (RAMS), Comprehensive Air Quality Model with Extensions (CAMx), and a new emissions inventory were used to study O3 formation downwind from the Israeli coast during summer 1997. While RAMS reproduced the observed diurnal variation of surface wind speeds and temperatures reasonably well, directions were somewhat less correlated. CAMx generally also reproduced the timing, location, and magnitude of measured surface and 300-m O3 max over Jerusalem, but also showed an even larger concurrent max over western Jordan, an area without observations. Observed near-zero nighttime surface O3 values, however, were over predicted because the CAMx grid was too large to accurately account for local emissions and titration effects. CAMx also generally accurately predicted another observed 300m local max near the Dead Sea, but could not account for a unique O3 depletion mechanism from bromine monoxide released from its water surface. Factor-separation analysis showed that transportation emissions produced 66% and 29% of the Jerusalem and Jordan 300-m simulated maxima, respectively, while power plant emissions produced about 35% and 62%, respectively. [Copyright &y& Elsevier]

A comparison of two separate MM5 land-use datasets (i.e., ‘US Geological Survey (USGS)’ and ‘Pollutants in the Atmosphere and their Transport over Hong Kong (PATH)’, each with different parameter values and different spatial distributions) was performed to understand the importance of land-surface processes and land-atmosphere interactions in the evolution of mesoscale weather phenomena during a high pollution episode in Hong Kong from 28 December 1999 through 1 January 2000. Also, a series of high resolution mesoscale numerical experiments was performed to investigate the possible roles of various surface characteristics or land-use parameters in this high pollution episode. Specifically, the relative importance of six land-use parameters including the roughness length, thermal inertia, soil moisture availability, albedo, surface heat capacity and surface emissivity are studied. Results from this study suggest that the soil moisture availability is the most important controlling parameter on the flow pattern and on surface fluxes. Sensitivity tests also show that the general flow pattern is insensitive to the other five land-use parameters [ABSTRACT FROM AUTHOR]

A receptor-oriented modelling system, consisting of a mesoscale meteorological model (RAMS) and a Lagrangian particle dispersion model (LPD) is applied to the determination of emissions of methane from livestock in agricultural regions in New Zealand. Aircraft measurements of methane mixing ratio profiles are input to the model, from which influence functions are obtained; these are the footprints of potential contributing emissions. Inversion techniques and statistical analysis enable the determination of confidence intervals for methane emissions. Results are compared with prior emissions data obtained by other methods.For two case studies in the Manawatu region of New Zealand in June 1995 and April 1997, methane emission fluxes of 54±32 and 56±54 mg m−2 d−1 are obtained (95% confidence intervals). These are consistent with independently estimated per-animal emission rates and observed livestock densities. For a field campaign in New Zealand''s Waikato region in 1999, where no emissions estimates were available a priori, the average emission fluxes derived using receptor-oriented techniques are 67±46 mg m−2 d−1.The error-bars on the emission fluxes are arguably quite large. This is due to uncertainties in the methane observations and errors in the meteorological simulations, which play a different role in each case study. Improvements in both the experimental and modelling procedures are proposed to reduce uncertainties in the calculated emission fluxes. [Copyright &y& Elsevier]

A global to regional modeling system has been developed to evaluate precipitation under doubled CO2. The National Centers for Environmental Prediction (NCEP) regional spectral model (RSM) is initialized and forced by current and doubled CO2 simulations from the NCAR community climate model (CCM3). Three RSM simulations, RSM0, RSM1, and RSM2, with resolution of 280, 50 and 15 km, are examined. The RSM0 setup resolution matches the T42 CCM3 simulations. The RSM2 simulation is centered over Taiwan. Due to incompatibility of the model physics, noticeable differences between RSM0 and CCM3 are found, especially in wintertime, which suggests that simulation from RSM0, rather than CCM3, should be used to contrast high-resolution regional variations produced by RSM1 or RSM2 simulations.While the spatial distributions of RSM1 and RSM2 simulations over Taiwan are greatly improved over the CCM3 simulation, the intensity of the unique wintertime drizzle is overestimated, especially in RSM2. There is also a spurious northward extension of the precipitation pattern from the subtropical warm-pool region. Thus the regional response to doubled CO2, which consists of more summerlike wintertime precipitation characteristics over the northeastern and eastern sides of Taiwan, with increased intensity mostly in the extreme events, is still in doubt and must be examined with improved global and regional models. [Copyright &y& Elsevier]

A mesoscale atmospheric model is used to model the break up of a morning air-temperature inversion during a clear weather situation with low wind speeds at ground. Modified slope-radiation parameterization in the model results in more realistic predicted air temperature profiles when compared to profiles measured with a tethered balloon. A wave number integration code is used to demonstrate how the modelled atmospheric profiles can be used to predict the reduction of sound level along ground during inversion break-up. [Copyright &y& Elsevier]

As applied to urban domains, traditional representations of surface albedo do not adequately account for the complex radiative exchange within the urban canopy. In this paper, we present a simple radiation model that takes into account the diurnal variation of short-wave radiation, including the effects of surface shading and radiation exchange among surfaces within the urban canopy. The model has been validated using prior observational studies and used to calculate the time-dependent effective short-wave reflectivity of hypothetical and case study urbanized grid cells, as well as the daily energy-weighted average of these parameters. Monte Carlo style simulations for four distinct urban land use categories indicate that the nadir-view albedo (NVA) typically underestimates daily solar radiative loads by 11–22%, depending upon the land use. We have also found that fairly detailed land-use classification schemes introduce large uncertainties in NVA. In fact, the uncertainty in albedo values for any urban land use category is comparable to the albedo variability across the various urban land use classifications. Furthermore, the magnitude of the diurnal variability of effective albedo for cities is large enough that neglecting it could adversely impact the ability to resolve the energy balance and circulation patterns associated with the urban heat island. [Copyright &y& Elsevier]

Maximum cross-correlation provides a method to remotely de-ter-mine high-ly re-solved three-dimensional fields of horizontal winds with e-las-tic li-dar through-out large volumes of the planetary boundary layer (PBL). This paper details the technique and shows comparisons between elastic lidar winds, remotely sensed laser Doppler velocimeter (LDV) wind profiles, and radiosonde winds. Radiosonde wind data were acquired at Barcelona, Spain, during the Barcelona Air-Quality Initiative (1992), and the LDV wind data were acquired at Sunland Park, New Mexico during the 1994 Border Area Air-Quality Study. Comparisons show good agreement between the different instruments, and demonstrate the method useful for air pollution management at the local/regional scale. Elastic lidar winds could thus offer insight into aerosol and pollution transport within the PBL. Lidar wind fields might also be used to nudge or improve initialization and evaluation of atmospheric meteorological models. [ABSTRACT FROM AUTHOR]

This work examines circulatory patterns of air pollutants in the area of Barcelona (Spain), a region with strong coastal and orographic influences. This was achieved through exploitation of elastic-backscatter lidar data and by numerical simulation of the atmosphere with a meteorological mesoscale model (MEMO). Lidar data were acquired in July 1992 during a collaborative campaign between Los Alamos National Laboratory (LANL) and the Polytechnic University of Catalonia (UPC). The lidar provided information about the distribution of aerosols and the prevailing winds, determined by application of a maximum cross-correlation algorithm to elastic-backscatter lidar data. Lidar winds are used to evaluate high altitude winds simulated by the model. This study showed that circulatory patterns in Barcelona are correlated with daytime convective vertical mixing, sea-breeze circulations, and vertical forcing caused by mountain thermal and mechanical effects. [ABSTRACT FROM AUTHOR]

The influence of vegetation and environmental conditions on the lake breeze and associated boundary-layer turbulence structure has been studied using a two-dimensional nonhydrostatic, compressible mesoscale model coupled with the SiB2 land-surface scheme. The results show that the impacts of vegetation on the lake effects are dependent on the environmental conditions, such as soil wetness and background wind, as well as vegetation characteristics. Both soil wetness and background wind play important roles in modifying lake effects on boundary-layer turbulence and the lake breeze, while the effects of vegetation type are secondary compared to the other factors. Without background wind, and under the same soil wetness, the maximum horizontal windspeed of the lake breeze is insensitive to the type of vegetation. Soil wetness can greatly affect both the maximum horizontal windspeed and the maximum vertical velocities of the lake breeze. With background wind, the lake-breeze circulations, upward motion regions, and boundary-layer turbulence structure all change markedly. A weaker background wind can strengthen the lake breeze, while stronger background wind suppresses the lake breeze circulations. The distribution of sensible and latent heat fluxes is also very sensitive to the soil wetness and background wind. However, for the same soil wetness (0.25 and 0.4 were chosen), there is only a small difference in the distribution of sensible and latent heat fluxes between the bare soil and vegetated soil or between the types of vegetated soils. [ABSTRACT FROM AUTHOR]

The semi-enclosed Mediterranean basin, surrounded by high mountains, is placed in a favorable location for cyclonic storms development. Most of these are extratropical cyclones of baroclinic and orographic origin, but occasionally, some low pressure systems may develop to assume features characteristic of tropical cyclones. Medicanes (MEDIterranean hurriCANES) are infrequent and small-sized tropical-like cyclones. They originate and develop over sea, and are associated with strong winds and heavy precipitations. Proper definitions and classifications for Medicanes are still partially lacking, and systematic climatic studies have appeared only in recent years. In this work, we provide climatologies of Medicanes in the Western Mediterranean basin based on multidecadal runs performed with the Weather Research and Forecasting regional model with different resolutions and setups. The detection of Medicanes is based on a cyclone tracking algorithm and on the methodology of Hart cyclone phase space diagrams. We compare the statistics of Medicanes in the historical period 1979–1998 between runs at a resolution of 11 km with different convective parameterizations and microphysics schemes and one run at a resolution of 4 km with explicitly resolved convection. We show how different convective parameterization schemes lead to different statistics of Medicanes, while the use of different microphysical schemes impacts the length of the cyclone trajectories. [ABSTRACT FROM AUTHOR]

Abstract: Obtaining realistic meteorological fields that are necessary for numerical modelling and prediction of sea state within operational oceanography as well as for Rapid Environmental Assessment (REA) tasks is not easy in the regions like the Adriatic Sea, which is surrounded by complex local orography. By analysing the output fields from the mesoscale meteorological model LAMI and the global ECMWF model between October 2005 and September 2006, this paper investigates effects that orography may exert on meteorological fields over the Adriatic region. The analysis is performed over four weather regimes typical for the Adriatic Sea, namely those characterized by bora, sirocco, bora–sirocco and etesian winds. Analysed are mean fields and mean differences between the two models. Results indicate that all investigated flow regimes are significantly affected by the Apennines and the Dinaric Alps, but also by smaller scale orography that is, at least along the Italian coast, adequately represented by LAMI and not by the ECMWF model. A kind of symmetry is found between sirocco and etesian regimes on the Adriatic scale, as well as on smaller scales, e.g. around the Gargano peninsula which acts as a typical 3D obstacle. Well known jets-and-wakes bora pattern along the eastern coast is clearly seen in the mean fields. The enhanced cloudiness and precipitation regions are shown to appear in convergence zones of bora, bora–sirocco and sirocco regimes, related to the mountain ridges perpendicular to the respective flow. Additionally, within the bora–sirocco regime a relatively narrow convergence zone at the boundary between the bora and sirocco flow is noticed. The authors believe that methods used in this paper can be useful when applied to other coastal regions and models. By considering the differences between output fields from two models of different resolution, the areas affected by smaller scale phenomena could be clearly seen. On the other side, the mean modelled fields show persistent meso to synoptic scale structures thus enabling better understanding of dynamical and climatological characteristics, both of the considered region and the models used. [Copyright &y& Elsevier]